A conventional power supply ought to have a bigger transformer, more capacitors and larger switches to provide a greater amount of current and power. To meet safety requirements, the circuit elements also have to be spaced from each other at a desired insulation distance, and provide sufficient space to disperse heat. All these make the printed circuit board holding the aforesaid circuit elements to be installed close to the casing of the power supply to better utilize the space while still maintain a safety distance from the casing. As the space between the printed circuit board and the casing usually is limited, installing the printed circuit board close to the casing is a tedious and time-consuming task.
To remedy the aforesaid problems, many techniques have been proposed in prior art. For instance, R.O.C. patent No. M290653 entitled “Printed circuit board fastening structure” provides at least one anchor strut beneath a printed circuit board and a bolt running through the printed circuit board to connect with the anchor strut. The printed circuit board is interposed between the bolt and the anchor strut. However, the bolt takes substantial space above the printed circuit board. Thus the circuit elements on the printed circuit board are even more crowded. Fastening installation also has to be performed manually inside the power supply. Hence it does not provide much improvement on printed circuit board fastening operation.
Another R.O.C. patent pub. No. 501860 entitled “Printed circuit board fastening structure” provides a plurality of spherical coupling elements each has an annular groove to be wedged by one of a plurality of anchor holes formed on a printed circuit board. And each spherical coupling element has a coupling portion connecting to a casing to anchor the printed circuit board. But wedging the printed circuit board in the annular groove of the spherical coupling element is troublesome. In the event that there is a fabrication error on the spherical coupling elements and the anchor holes, coupling them is even more difficult. Moreover, the spherical coupling elements also have to be installed inside the power supply and fastened to the printed circuit board from an inner side towards the outer side. All these create a lot of problems for manual installation.
Yet another R.O.C. patent No. M311220 entitled “Printed circuit board fastening structure” has a printed circuit board with a plurality of anchor holes formed thereon. Each of the anchor holes has a notch of varying diameters. A plurality of anchor elements are provided to be wedged in the notches to form anchoring. But the anchor elements could be loosened off from the notches. Hence it also provides an elastic detent unit to enhance anchoring of the printed circuit board. Such an approach requires forming the notches on the printed circuit board at a greater size, and results in wasting of the precious area of the printed circuit board. To prevent loosening off, an extra ancillary mechanism has to be provided to anchor the printed circuit board. Hence it also has the drawbacks of wasting space and higher cost.
Other similar techniques can be found in R.O.C. patent publication Nos. 445023 and 508049, and R.O.C. patent Nos. M304187, M329946, M332139 and M333752. They all have the problems mentioned above, such as occupying more space, higher costs, and difficult installation from the inner side to the outer side. There are still rooms for improvement.